Carbon fiber, fiberglass, or what?

Discussion in 'Composites' started by pequeajim, Jan 31, 2007.

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  1. Jan 31, 2007 #1

    pequeajim

    pequeajim

    pequeajim

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    I am looking at purchasing a new aircraft.

    So far my choices have primarly limited to composite aircraft. I attached a few links for reference, not to compare the aircraft, but as an example of different types of glass construction. Two, of glass and and carbon fiber, and the Arion primarly of glass.

    http://www.arionaircraft.com/

    http://www.sportaircraftworks.com/oto%20bin/DYNAMIC.htm

    http://www.flightdesignusa.com/

    I really like the Arion Lightning, but would be interested in discussing construction techinques, and the ability of a primarly all glass aircraft to hold up over time?
     
    Last edited: Jan 31, 2007
  2. Feb 2, 2007 #2

    orion

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    This is sort of a difficult subject to discuss without knowing the details of the airplanes' design processes. To make a general comment, if each airframe was designed correctly for the loads and materials, then there is no reason why any one material would be better than any other. Other general comments are:

    1) Any structure that uses Kevlar will be virtually impossible to repair - at least with tools that most homebuilders will have. furthermore, Kevlar is susceptible to contamination since as an organic fiber, it can absorb or wick moisture. Temperature changes could the affect the absorbed moisture in such a way as to damage the aesthetic or even the structural integrity of the part.

    2) Fiberglass is common, easy to work with and has the largest application (of the composite materials) to the homebuilt industry. The drawback however is that fiberglass is subject to fatigue issues - its S-n curve is virtually identical to that of aluminum. If the designer(s) know this and account for it in the engineering/design process then there is no reason not to choose an airplane constructed of it. The problem though is that not all designers know this and many are still foolishly thinking that fatigue does not affect fiberglass structures (it is glass after all!).

    3) Graphite is my own favorite, primarily due to its physical properties and working characteristics. The material is very resistant to fatigue, even in woven form, and provided a correct resin is chosen, can create a pretty tough component. But graphite is of course more expensive, can exhibit brittle properties (susceptible to crack propagation), and is not as durable in its application, especially in very light structures.

    I don't know if any of this helps - if you have any questions, well, you know what to do.
     
  3. Feb 2, 2007 #3

    pequeajim

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    Thanks Orion... I was hoping that you would reply. I appreciate the knowledge that you bring to the forums. I think my biggest concern is in the Lightning's wing spar is made up of fiberglass with some carbon fiber layered in where the spar connects with wing root. They also use what looks like a strip of composite wood material in the center of the spar, (see pic).

    I wonder how well this will hold up over time, especially when this aircraft flys at around 170-180mph?

    I can see it holding up to some hefty loads now, but what about 500-1000 hours from now?

    I love the aircraft, but am leary of something that I really don't understand.
     

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  4. Feb 2, 2007 #4

    orion

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    I actually wrote up a quick review of this one on another thread herein, just based on the information and pictures they posted at their site. In short, I saw several red flags - I'd approach this one with extreme caution.
     
  5. Feb 2, 2007 #5

    Topaz

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    Love the barbeque in the (near) background.

    Nice workshop. :speechles
     
  6. Feb 2, 2007 #6

    pequeajim

    pequeajim

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    LoL! Actually, to be fair, this was a wing panel that I dragged out in the room from the workshop at one of their dealers so that I could get some decent light.

    (boy, I should have thrown some ribs on there while I was at it!) ;)
     
  7. Feb 4, 2007 #7

    macosxuser

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    Looks like a thin spar attach for +/- 5G's. Is that ultimate load they are quoting?
     
  8. Feb 27, 2007 #8

    wsimpso1

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    The material set, particularly once within composites, should matter if you are building in it, but in a complete airplane, what matters is how it flies, how durable it is, and how reliable it is.

    Details in a design are everything. Just because they have wood in the cores at the hard points is not in and of itself a bad thing. There are a lot of Long Eze's, Cozy's and their derivitives flying around with laminated wood cores in spars at the hard points. The fact that Orion is concerned about how they were done in this design bears merit. I would look up the thread Orion contributed to...

    Billski
     
  9. Jan 5, 2015 #9

    Chlomo

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    Well as of 2015 only Flightdesign is in good standing of above 3.
     
  10. Jan 5, 2015 #10

    autoreply

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    Aerospool Dynam8c still does fine too.
     
  11. Jan 10, 2015 #11

    Magnus Wallner

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    Why would it be a concern to use wood (assuming of course that the design is correct to begin with)? In many other areas involving composites it's a quite common practice (think boats).
     
  12. Jan 10, 2015 #12

    autoreply

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    Boats don't see anywhere near the critical loads airplanes do.


    Aircraft-grade wood is certainly a good material to build aircraft. It is however rare and very expensive, often more so than CFRP. Taking none-aircraft-grade wood is IMHO beyond stupid unless you really know what you're doing (and grade yourself)
     
  13. Jan 10, 2015 #13

    Magnus Wallner

    Magnus Wallner

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    I'm only talking about aircraft grade materials. I'm just curious as to why (if) there is an inherent problem in mixing wood and FRP on aircraft given that it's such a common procedure elsewhere.
     
  14. Jan 10, 2015 #14

    autoreply

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    "Because that's how we always do it". 90% of these kind of choices/habits are opinion, not objective decisions.
    Price and availability are real issues however and the reason several manufacturers (Extra, Scheisse) are replacing wood parts with composite parts.


    Structurally they're a good match and plenty of planes use them combined. As long as the wood is sealed (water) and of aircraft grade, most combinations work just fine. A CFRP/balsa/CFRP skin is unbeatable for weight for example.

    Plenty of composite sailplanes with wooden parts in them that've done perfectly fine for 50 years.
     
  15. Jan 10, 2015 #15

    Magnus Wallner

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    I was under the impression that Kevlar (aramid) was a synthetic fiber, no? It's used quite much in protective clothing, mainly for motorcycle use, and in such applications the fiber is very exposed to humidity, both from weather and body moisture. Not to mention sails. Or is it mainly a problem when combined with a matrix?

    And why is a Kevlar reinforced structure harder to repair compared to carbon or glass?

    Edit: found an interesting report here http://web.mit.edu/roylance/www/allred_83.pdf
     
  16. Jan 10, 2015 #16

    autoreply

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    Unfortunately Orion passed away.

    All aramids are synthetic (man-made) and organic (carbon-based).

    Kevlar is a Para-Aramide, not to be confused with a Meta-Aramide like Nomex.

    Those and most other aramides are hygroscopic as hell. Expose them to moisture and they'll suck it up.

    In a structure it HAS to be coated, preferably also embedded in a layer of glass or carbon to avoid it sucking up moisture (which will swell the structure and delaminate it catastrophically once frozen)

    Cutting, sanding, abrading Kevlar is a nightmare. It's like sanding chewing gum.

    Scissors work reasonably well on Kevlar, so cut it in the mold to the right size, because you'll regret leaving it oversized and having to sand it down...
     
    BoKu and Norman like this.
  17. Jan 10, 2015 #17

    kent Ashton

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    To add to Autoreply's non-autoreply: sanding Kevlar results in a fuzz that can't be sanded away like fiberglass can. When I have seen Kevlar used, you would usually put a layer of fiberglass over it and do your sanding on that.

    Another thought about wood and fiberglass. I would guess it is similar to the problem of combining fiberglass and carbon fiber in the same structure. The weaker material gives and the stronger material takes the load so the fiberglass is just along for the ride until the CF fails.
     
  18. Feb 4, 2015 #18

    tunnels

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    So don't mix materials !! what you start with you carry on with to the end !! Kevlar is very abrasive resistant and does not make stiff panels ! Carbon is stiff but breaks easy just like carrot ! glass with Vinylester resin is all that's needed !!
     
  19. Feb 5, 2015 #19

    NoStealth

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    post rating identification and comment system
    spellyng,punctuationne&grammr: intensionally baaad..check
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    analysis: probably a banned member annoy troll, please stop feeding
     
  20. Feb 5, 2015 #20

    Jan Carlsson

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    Aj lowe itt !!!
     

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